1. Field of the Invention
The present invention relates to a direct injection-type spark ignition engine that supplies a fuel directly to the inside of a combustion chamber.
2. Prior Art
In conventional direct injection engines, the injector is provided at an angle from 20 to 50 degrees with respect to the horizontal face of the combustion chamber, under the air intake ports thereof.
These engines are constructed so that during stratified combustion, a fuel is injected towards the cavity provided in the piston and then an air-to-fuel mixture is ignited by being introduced into the ignition plug located in the upper center of the combustion chamber, in combination with the air flow created by the flow creation means, such as swirl control valve, that is located at the intake ports.
Japanese Application Patent Laid-Open Publication No. Hei 06-42352 describes art by which, in a center injection type of direct injection gasoline engine having an injector in the central top of the combustion chamber and injecting the fuel towards the piston, the ignition plug is struck directly with sprays of fuel and the density of the air-fuel mixture is controlled with high accuracy.
Japanese Application Patent Laid-Open Publication No. Hei 10-131756 describes an engine which, as with the above art, is provided with an injector for injecting a fuel from nearly the top center of the combustion chamber towards the piston, with a cavity in the valve portion at the top of the piston, and with an ignition plug at where it is offset both inside the cavity and at the air intake valve end. Since the ignition plug is located so that sprays of fuel do not directly strike the plug, the shape of the piston and the flow of air ensure intensive supply of the mixture to the ignition plug and stabilize stratified combustion.
However, for the center injection type of direct injection gasoline engine described in Japanese Application Patent Laid-Open Publication No. Hei 06-42352, since the ignition plug is struck with the fuel directly and actively, consideration is not given to the occurrence of a misfire due to the sticking of a liquid fuel to the plug, or to the deterioration of combustion stability, associated with the misfire.
In addition, for the center injection type of direct injection gasoline engine described in Japanese Application Patent Laid-Open Publication No. Hei 10-131756, since the piston shape and the flow of air are optimized to stratify the mixture, the occurrence of unburnt hydrocarbon, soot, and the like due to the combustion of any fuel components sticking to the piston is likely to deteriorate exhaust performance. Furthermore, there are the problems that a flow creation means, piston machining, and sophisticated control are required and that the costs are high.